The objective of this project is to use a retrovirus-based rodent model system to understand the interaction of retroviruses with brain capillary endothlial cells (CEC) and determine the molecular basis of retrovirus-induced neurological disease. PVC-211 murine leukemia virus (MuLV), a variant of the erythroleukemia-inducing Friend MuLV, causes a rapid neurodegenerative disease when injected into newborn rats and mice. We have previously shown that PVC-211 MuLV is significantly more infectious to brain CEC than Friend MuLV and that infection of CEC is necessary for induction of neurodegenerative changes in the brain. In an attempt to determine how PVC-211 MuLV infection of brain CEC results in the death of neurons, we are carrying out studies to determine if the virus is inducing inflammatory cytokines or neurotoxins. Since PVC-211 MuLV is unique among mouse ecotropic MuLVs in its tropism for brain CEC, we have also been carrying out studies to determine the genetic changes that have occurred in the virus to alter its cellular tropism. Using chimeric viruses between PVC-211 MuLV and Friend MuLV, we have shown that as few as two amino acid changes in the envelope protein of PVC-211 MuLV are responsible for its CEC tropism. These viral determinants were also shown to extend the host range of PVC-211 MuLV to hamster cells, which are normally resistant to ecotropic murine leukemia viruses. Further studies indicated that PVC-211 MuLV can also efficiently infect CEC of other organs, such as liver, kidney and heart, when inoculated into neonatal rats, as well as infect primary explant cultures of CEC derived from both the liver and brain of adult rats. These observations suggest that PVC-211 MuLV may be a useful tool for in vivo or ex vivo gene transduction into CEC. In preparation for testing PVC-211 MuLV as a tool for endothelial cell-targeted gene therapy, we have established a protocol for efficient infection of cultured CEC with the virus. Using a chimeric virus between PVC-211 MuLV and Friend MuLV that is CEC-tropic, but not neuropathogenic, we are attempting to transduce various genes into CEC in order to test the efficacy of CEC-based gene therapy for controlling tumor growth in vivo.